A runaway seven-year-old girl slipped through security checks at Geneva's airport and onto a plane without a ticket before being spotted by a crew member and handed over to police, officials said on Wednesday.

Acknowledging an "eminently regrettable" incident that could have turned out worse, Geneva airport spokesman Bernard Stampfli said authorities were enhancing measures to make sure that children are accompanied by adults when passing through security checks at the small airport along the French border.

In the incident on Sunday, the girl, who was not identified, initially slipped away from her parents at Geneva's main railway station and travelled by train to the airport.

The girl repeatedly "took advantage of her small size" and employed a "ruse" to make it look like she was travelling with adults ahead or behind her, he said.

After a first attempt failed, she tried again and succeeded, getting aboard an easyJet flight to Corsica.

Mr Stampfli said an alert crew member from Air France, who had spotted the girl trying to board one of its flights, flagged her to the crew of the low-cost carrier which in turn alerted police.

Using video surveillance footage, airport authorities said she was turned away after trying to follow crew members onto a flight. She then quickly blended into the nearby crowd, pretending to join up with her parents, Mr Stampfli said.

The second time, she succeeded by slipping through a gap only large enough for a small child.

EasyJet, in a statement, acknowledged that "an unaccompanied child incorrectly boarded flight EZS1305 from Geneva to Ajaccio", and said an investigation has been launched.

"The crew correctly identified the child should not be onboard and immediately reported it to the police," the statement said.

Geneva airport's Mr Stampfli said representatives of all airport personnel were immediately summoned for a meeting.

"What this shows is that while controls for adults and accompanied children are effective, there are holes to fill when it comes to unaccompanied children," he said.

New measures include confirming that children are accompanied by at least one adult at security checks, he said.